Art of grinding



W. PEASLEE ART OF GRINDING July 3, 1934.

Filed 001;. 11. 1930 Patented 1.1.3, 1534 UNITE-l) s T'ATE'S PATENT OFFICE 1,965,256 I ART OF Gl tl NDING Application October 11,

2 Claims.

This invention relates to improvements in the art of grinding.

In the past, grinding wheels having a uniform density from their outer peripheries to the centers thereof have been employed, which wheels were rotated at a constant speed throughout their life. These wheels when new and unworn have a definite cutting action for a given peripheral speed and would remove a definite amount of stock per cubic inch of grinding wheel wear. As the wheels wore and were redressed the stock removal per cubic inch of wheel wear decreased materially. In other words, a grinding wheel of a certain grade acted as a softer wheel toward the center thereof and would crumble away at a rapid rate, so that a relatively few number of work pieces could be ground or a comparatively short period of time elapsed between retruing operations.

It is, therefore, one of the principal objects of the present invention to provide an improved grinding wheel which will have substantially the same cutting action per cubic inch throughout its life at a given R. P. M.

Another object of the invention is the provision of a grinding wheel having a variable stock removing capacity from the outer peripheral face to the center thereof due to the varying peripheral speed of the wheel as it is worn and trimmed away.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification considered in conjunction with the accompanying drawing forming a part thereof, and it is to be understood that any modifications may be made in the exact structural details there shown and described, within the scope of the appended claims, without departing from or exceeding the spirit of the invention.

In the drawing:

Figure 1 is a front elevational view of a semiautomatic grinding machine including the improvement of this invention.

Figure 2 is a longitudinal sectional view of the abrasive wheels of the machine shown in Figure 1.

Throughout the several views of the drawing similar reference characters are employed to denote the same or similar parts.

As was noted above, grinding wheels are subject to constant wear when in use and must be trimmed or trued periodically to maintain a proper cutting face on the wheel. The grinding wheels are generally carried by shafts or spindles which are rotated at a constant R. P. M.

1930, Serial No. 488,078

this it will be seen that a new unworn grinding wheel will have a definite peripheral speed and as the wheel is worn and trimmed away the said peripheral speed will necessarily decrease in proportion to its diameter. It has been found that in practice that a given grade of wheel rotating at a high or normal peripheral speed has a definite stock removal capacity per cubic inch of wear on the wheel, while as the wheel decreases in size or as its peripheral speed decreases the wheel acts soft and crumbles away at a rela-' tively rapid rate so that its stock removal action or capacity decreases to a large extent per cubic inch of wheel wear. This crumbling and rapid wearing away of the wheel necessitates constant redressing operations on the work which materially shorten the life of the wheel and increases the cost of production thereof.

In order to overcome the above mentioned difficulties and to remove the same amount of stock from work pieces with a worn wheel as with a new wheel per cubic inch of wheel wear, I have provided a grinding or abrasive wheel of varying stock removing capacity. The wheel is so con structed and arranged that at the center thereof the same amount of stock is removed per cubic inch of wheel wear at a relatively slower peripheral speed as was removed when the wheel was new and rotated at a higher peripheral speed, it being understood that the shaft or spindle carrying the wheel is actuated at a constant B. P. M.

A wheel for producing this result may be obtained in several ways: first, by varying the density of the wheel, second, by varying the grain size of the wheel, and third, by changing or varying the abrasive material used in the wheel. In the first method the center of the wheel would be quite hard or very dense gradually softening or becoming less dense as it approaches the outer periphery of the wheel. This varying density would afford the same cutting action at any point thereof at a given R. P. M. so that the stock removal in a given period would be substantially the same even though the linear travel of the several points of the wheel varied greatly.

In the second method, namely: by varying the grain size of the wheel, the faster cutting grains would be positioned at the center of the wheel, with the less fast cutting grains graduated from the center toward the outer peripheral surface. A wheel made by this method would likewise remove the same amount of stock from the worl: for a given period of time at the same P. M. irrespective of its circumferential linear travel.

The same results would be obtained from the third method in which the faster cutting abrasive materials would be positioned in or around the center of the mass of the wheel and would graduate from there to the outer peripheral edge of the wheel. In each of these methods it is to be understood that the peripheral face of the wheel and the stock removal quality throughout its life would remain at the recognized efficient point..

As shown in Figure 2 of the drawing, the grinding wheel 10 has an active peripheral face 11 having a definite stock removal capacity at a given speed which stock removing capacity is constantly increased as the wheel is worn and trimmed away until it reaches its innermost portion 12. This wheel 10 may be employed with any type of grinding machine, and as shown in Figure 1, there has been chosen for illustrative purposes a centerless grinder which is semi-automatic in its action. The grinding wheel 10 is secured to the end of a spindle l3 journaled on the bed 14 and rotatable at a constant speed by a prime mover or motor 15 carried by the bed 14. Transmission belts, or the like, 16 extend from the prime mover 15 to a jack shaft 1'7 from which additional transmission mechanism 18 extends to the spindle or shaft 13 for rotating said spindle at a constant speed. For truing the active face of the wheel, the grinding wheel guard or housing 19 has mounted thereon for movement relative thereto across the face of the wheel, a truing tool mechanism 20 operable by a hand wheel 21. To feed the tool into the wheel a knob or the like 22 is provided. The bed 14 supports, for movement longitudinally thereof, a work controlling and feeding mechanism comprising a slide 23 supporting the bracket 24 for regulating wheel spindle 25 on which is secured the regulating wheel 26. The active faces of the wheels 10 and 26 are spaced from one another to provide a grinding throat in which the work to be operated upon is positioned. The said work 27 is peripherally supported by a work rest blade 28which subtends the grinding throatand is supported in adjustable positions by work rest block 29.

The slide or housing 23 is fed toward the grinding wheel 10 to feed the work 27 into the grinding wheel. For this purpose an adjusting screw 30 is rotatably but not translatably carried by the bracket 31 secured to the bed 14. A nut 32 is carried by the housing or slide 23 and has secured thereto a handle 33 for rotating same and feeding it and the slide and parts carried thereby toward the grinding wheel. The said lever or handle 33 has a definite path of movement, for example, 90 degrees from the vertical, as shown in Figure 1, to the horizontal position and back again for alternately feeding and retracting the slide 23.

The operation of the machine shown in Figure 1 is as follows, assuming the grinding throat to be enlarged to permit the insertion of a work piece on the work rest blade 28, the handle or lever 33 is then actuated toward the'-op'erator, or toward the front of the machine for partially rotating the nut 32 and feeding the slide and parts carried thereby including the work piece toward the grinding wheel to effect a stock removal from the work piece. After the handle has been actuated to the limit of its travel it is held in this position to permit a dwell in the movement of the work to produce the proper finish thereon and allow a sparking out of the grinding wheel. The handle is then returned to its normal position to retract the slide and parts carried thereby to their normal work receiving position whereupon the finished work piece is replaced by an unfinished one and the cycle of operation repeated.

The actuation of the lever or handle 33 through its feeding arc requires substantially the same time period for each work piece. From this it will be seen that a new grinding wheel of a uniform density rotating at its most efficient peripheral speed will remove a definite amount of stock in a given time period without appreciable wear on the grinding wheel and without an appreciable damage to the cutting face thereof. But as the wheel wears it's peripheral speed decreases thereby reducing the stock removing efliciericy of the wheel for the same time period and the wheel acts as a softer wheel crumbling away at a relatively rapid rate while rotating at the same speed as the new wheel. With the grinding wheel illustrated and described herein the stock removing efficiency of the wheel is uniform throughout life and at any point thereof since as the wheel wears and becomes smaller in diameter its cutting action acts as a harder wheel than the new wheel since the peripheral speeds of the new and worn wheels vary.

What is claimed is: i

1. A grinding wheel for operation at a constant prescribed number of revolutions per minute, comprising a composition of an abrasive material and a bond therefor, the grit and grade of the composition material progressively, continuously decreasing from center to the periphery of the wheel whereby the wheel when operated at constant R. P. M. will perform a prescribed grinding irrespective of reductions in diameter of the wheel resulting from wear, truing or the like.

2. Agrinding wheel for use in precision grinding work and for operation at a constant number of revolutions per minute irrespective of the existing diameter of the wheel, comprising composition of an abrasive material and a bond therefor, the grit and grade of the composition material progressively, continuously varying from center to periphery of the wheel inversely as the radial dimension thereof whereby the cutting action of the wheel for a given R. P. M. will remain constant irrespective of variations in diameter of the wheel due to wear, truing or the like.

WILLETIS PEASLEE. 

